CUDA 7.0 requires compute capability 2.0 or higher (sm_20 or later). The GTX 285 is an sm_13 device, so you cannot use it with CUDA 7. Unless you need CUDA 7.0 specific features, an alternative would be to download CUDA 6.5, which only requires compute capability 1.1 or higher (sm_11 or later). If you go down that route, make sure you also install a matching driver package, since support for pre-sm_20 GPUs was removed in drivers several months ago.
In general, with finite engineering resources, it makes sense that support for old hardware must be retired in newer software that is required to support new hardware. In this case, the removal of support for pre-sm_20 devices happened at the graphics driver level several months prior to the release of CUDA 7.0. Since CUDA must co-operate with the graphics driver (e.g. for GPU resource allocation), the latest version simply cannot support hardware predating sm_20 at this time.